Fugitive core tooling and method

ABSTRACT

A ceramic core is produced by introducing a fluid ceramic core material, such as a ceramic slurry, into a core-shaped cavity formed at least in part by one or more fugitive core tooling liners residing in a back-up body, removing the ceramic core from the cavity, and removing the one or more fugitive tooling liners from the back-up die body and discarding them. The fugitive tooling liners and optional tooling inserts are used in one or more production cycles (e.g. ceramic slurry injection cycle) to make a single or multiple ceramic cores and then replaced with fresh (un-used) tooling liners and optional inserts to make other ceramic cores.

FIELD OF THE INVENTION

The present invention relates to manufacture of a ceramic core for use in casting a hollow metallic article, such as a hollow turbine components, and more particularly, to tooling and a method for making a ceramic core.

BACKGROUND OF THE INVENTION

Most manufacturers of gas turbine engines are evaluating advanced multi-walled, thin-walled superalloy gas turbine airfoils (i.e. turbine blade or vane) which include intricate air cooling channels to improve efficiency of airfoil internal cooling to permit greater engine thrust and provide satisfactory airfoil service life. U.S. Pat. Nos. 5,295,530 and 5,545,003 describe advanced multi-walled, thin-walled turbine blade or vane designs which include intricate air cooling channels to this end.

In casting hollow gas turbine engine blades and vanes (airfoils) and also shrouds having internal cooling passageways, a fired ceramic core is positioned in a ceramic investment shell mold to form internal cooling passageways in the cast airfoil. The fired ceramic core used in investment casting of hollow airfoils typically has an airfoil-shaped region with a thin cross-section leading edge region and trailing edge region. Between the leading and trailing edge regions, the core may include elongated and other shaped openings so as to form multiple internal walls, pedestals, turbulators, ribs, chambers, plenums, and similar features separating and/or residing in cooling passageways in the cast airfoil or cast shroud.

The ceramic core typically is formed to desired core configuration by injection molding, transfer molding or pouring of an appropriate fluid ceramic core material that includes one or more ceramic powders, a binder, and optional additives into a suitably shaped core molding die. After the green molded core is removed from the die, it is subjected to firing at elevated (superambient) temperature in one or more steps to remove the fugitive binder and sinter and strengthen the core for use in casting metallic material, such as a nickel or cobalt base superalloy typically used to cast gas turbine engine blades and vanes (airfoils).

Conventional core tooling requires expensive EDM machining for hardened tool steel permanent tooling and sophisticated machining techniques for tooling dies and tooling inserts, ribs, inserts, and other cooling features to be imparted to the core formed using the tooling. Unfortunately, the ceramic core materials are abrasive to tooling and result in wear of the tooling over time. Such tooling wear produces undesirable changes and inconsistencies in core geometry and performance of castings made with the cores over time.

The fired ceramic core then is used in manufacture of the shell mold by the well known lost wax process wherein the ceramic core is placed in a pattern molding die and a fugitive pattern is formed about the core by injecting under pressure pattern material, such as wax, thermoplastic and the like, into the die in the space between the core the inner die walls. The pattern typically has an airfoil-shaped region with a thin cross-section trailing edge region corresponding in location to trailing edge features of the core. The pattern also can include other features such as including, but not limited to, one or more platforms, shrouds and the like.

The fugitive pattern with the ceramic core therein is subjected to repeated steps to build up the shell mold thereon. For example, the pattern/core assembly is repeatedly dipped in ceramic slurry, drained of excess slurry, stuccoed with coarse ceramic stucco or sand, and then air dried to build up multiple ceramic layers that form the shell mold on the assembly. The resulting invested pattern/core assembly then is subjected to a pattern removal operation, such as steam autoclaving, to selectively remove the fugitive pattern, leaving the shell mold with the ceramic core located therein. The shell mold then is fired at elevated temperature to develop adequate shell mold strength for metal casting.

Molten metallic material, such as a nickel or cobalt base superalloy, is cast into a preheated shell mold and solidified to produce an equiaxed grain, columnar grain or single crystal airfoil. The resulting cast airfoil includes the ceramic core therein so as to form internal cooling passageways upon removal of the core. The core can be removed by leaching or other conventional techniques, leaving a hollow cast metallic airfoil.

SUMMARY OF THE INVENTION

The present invention provides tooling for making a ceramic core wherein the core tooling employs one or more fugitive tooling liners and optional fugitive tooling inserts that are placed in a simple-geometry back-up or support body in a manner to form at least a portion of a core-shaped cavity and that eliminate the need for costly hardened/machined permanent steel tooling.

In an illustrative embodiment of the invention, each fugitive tooling liner includes an outer surface having a simple geometry to conform to that of an adjacent inner support surface of the back-up body and an inner surface that is configured to form desired core surface features when the tooling liners are placed in the back-up body with the tooling liners forming the core-shaped cavity. Optional fugitive inserts can be placed between the tooling liners to form ribs, holes, passages and other features on and/or in the ceramic core. The core-shaped cavity may have one or more airfoil-shaped surfaces in the production of a ceramic core for use in casting of a hollow airfoil, such as a hollow gas turbine blade or vane, or other hollow article.

A ceramic core is produced pursuant to a method embodiment of the invention by introducing a fluid ceramic core mixture typically under pressure into the core-shaped cavity formed at least in part by the fugitive tooling liners in the back-up body, removing the molded ceramic core from the cavity, and removing the fugitive tooling liners with the core or from the back-up die body (separately from the core) for discarding. The next ceramic core is produced using fresh (un-used) tooling liners and optional tooling inserts. Alternately, the fugitive tooling liners may be left in the back-up body and reused if the liners are in acceptable condition to this end. That is, the fugitive tooling liners and inserts are used in one or more production cycles (e.g. ceramic slurry injection cycles) to make a single ceramic core and then replaced with fresh (un-used) tooling liners and optional inserts.

Other advantages of the present invention will become more readily apparent from the following detailed description taken with following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of tooling in accordance with an illustrative embodiment of the invention where facing tooling liners are employed.

FIG. 1B is a cross-sectional view of tooling in accordance with another illustrative embodiment of the invention where facing tooling liners are employed to form only portions of the core molding surfaces and the back-up body surfaces form the remaining portions of the core molding surface.

FIG. 2 is a cross-sectional view of still another embodiment of the invention wherein various types of fugitive inserts are placed between facing tooling liners.

FIG. 3 is a perspective view of a core with fugitive liners/inserts wherein the core resides between facing fugitive tooling liners after removal from the back-up body.

FIG. 4 is a perspective view of a core with the fugitive liners/inserts removed.

FIG. 5 is an exploded view of the back-up bodies with the fugitive tooling liners and inserts between the liners showing where the inserts are pre-located into the liners.

DESCRIPTION OF THE INVENTION

The present invention provides tooling for making a ceramic core wherein the tooling employs one or more fugitive tooling liners and optional fugitive tooling inserts that are placed in a simple-geometry back-up or support body in a manner to form at least a portion of a core-shaped cavity and that eliminate the need for costly hardened/machined permanent steel tooling. Although the invention is described in detail below with respect to making a ceramic core having an airfoil shape for use in casting metallic airfoils, such as gas turbine engine blades and vanes, it is not so limited and can be used to make a ceramic core having any desired shape.

Referring to FIGS. 1-5, an illustrative embodiment of the invention provides tooling including a back-up or support body 10 and multiple fugitive tooling liners 20 a, 20 b disposed in the back-up body 10 to form at least a portion of a core-shaped cavity C.

The back-up body 10 comprises multiple parts (first and second parts 10 a, 10 b shown) positionable to form a tooling cavity TC to receive the tooling liners 20 a, 20 b. The multiple parts of the back-up body can be incorporated and positioned as an injection die of a conventional core injection machine.

Referring to FIGS. 1A, 1B and 5, the parts 10 a, 10 b of the back-up body 10 include interior flat and curved geometry surfaces 10 s so as to provide a simple geometry that is not costly to machine. Although particular simple flat and curved surfaces 10 s are shown, surfaces 10 s of other simple geometry can be used including, but not limited to, easily-machined surfaces which are all curved or all flat, or a combination thereof, as well as other easy-to-machine surface profiles. The back-up body can be made of hardened steel or other material that can withstand the pressure of the liquid ceramic material introduced typically under pressure to form the ceramic core.

In FIG. 1A, all core surfaces will be formed by the inner surfaces of the tooling liners 20 a, 20 b. However, the invention is not limited to this embodiment since simple surfaces of the core-shaped cavity and thus the core may be formed by surfaces of the permanent tooling; i.e. by surfaces BS on the back-up parts 10 a, 10 b, as shown in FIG. 1B. Also, a single tooling liner 20 a or 20 b may be employed for simple core surfaces.

The core tooling includes one or more fugitive tooling liners 20. For purposes of illustration, the core tooling is shown including first and second fugitive tooling liners 20 a 20 b that are placed in the tooling cavity TC. Each first and second tooling liner includes an outer surface 20 s having a simple flat and/or curved or other simple geometry to conform to or match that of an adjacent inner support surface 10 s of an adjacent part of the back-up body 10 and an inner surface 10 c that is configured to form desired core surface features when the tooling liners 20 a, 20 b are placed in the back-up body 10 in facing relation to form the core-shaped cavity C. Although the tooling liners are shown including flat and curved outer surfaces 20 s that mate with an adjacent flat and curved surface 10 s of the back-up body, other simple surfaces 20 s can be used that match or mate with those of the adjacent parts of the back-up body 10. The tooling liners 20 a, 20 b can be designed to snap-fit into place in the parts 10 a, 10 b of the back-up body 10, or they can be held by releasable adhesive or releasable fasteners or clamps.

The inner surfaces 20 c of the tooling liners form an air-foil core-shaped cavity C therebetween, FIG. 1A, or at least a portion of the air-foil core-shaped cavity C, FIG. 1B, when the tooling liners 20 a, 20 b are placed in the back-up body 10. As mentioned above, simple surfaces of the core-shaped cavity C and thus the core may be formed by surfaces BS of the back-up parts 10 a, 10 b, as shown in FIG. 1B. The inner surfaces 20 c are configured to form desired core surface features when the tooling liners 20 a, 20 b are placed in the back-up body 10 in facing or other relation to form at least a portion of the airfoil core-shaped cavity C.

The fugitive tooling liners typically are injection molded to shape using a suitable polymer, although other fugitive liner materials can be used including, but not limited to, polylactone, polyvinyl, and starch-modified polymers.

The core tooling can include one or more optional fugitive inserts 30 a-30 h placed between the tooling liners 20 a, 20 b and/or on the inner surfaces 20 c of the tooling liners 20 a, 20 b, FIGS. 2 and 5. The inserts 30 a-30 h extending between the tooling liners can be used to form holes, passages and other through-openings in the ceramic core. The inserts 30 a-30 h disposed on the surface 20 c of the tooling liners can be used to form core surface features such as ribs, channels, shrouds, chambers, back-locked features (e.g. a dovetail joint) not easily formed in a complicated end product core.

The fugitive inserts alternately can be provided as fugitive subassemblies where different inserts are provided in one subassembly to form through-passages and core surface features as shown for inserts 30 a and 30 b in FIG. 2. The fugitive inserts can be injection molded on the liner surface 20 c as shown for insert 30 h in FIG. 2, or as part of the liner surface as shown for insert 30 g in FIG. 2. The inserts 30 a, 30 b can be assembled from separately injection molded insert elements and located on the liner surface 20 c. The fugitive inserts can comprise or be incorporated as a part of the final molded core to produce a composite core having certain fugitive features such as spacers, layers, through-extending fastener, and the like for use in subsequent investment mold forming processing.

The fugitive inserts can include connection features to the liner surface 20 c that may be normal (perpendicular) to the liner surface 20 c as shown for insert 30 d in FIG. 2. The fugitive inserts can also include connection features to the liner surface 20 c that may be normal (perpendicular) to the parting plane PP of the cavity C as shown for inserts 30 e, 30 f in FIG. 2.

A ceramic core is produced pursuant to a method embodiment of the invention by introducing a fluid ceramic core material, such as a ceramic slurry, typically under pressure into the core-shaped cavity C formed by the fugitive tooling liners 20 a, 20 b in the back-up body 10. The fluid ceramic material is introduced via a passage CP (FIG. 1B) in the back-up body 10. After the ceramic core is molded and set, the molded green (unfired) core is removed by opening the parts 10 a, 10 b of the back-up body 10 and removing the molded green ceramic core. The fugitive tooling liners 20 a, 20 b are removed from the back-up die body with the molded green ceramic core, FIG. 3, or separately from the molded green core and then discarded (not re-used). The optional fugitive inserts 30 a-30 h can be removed from the molded green ceramic core by thermal treatment to melt and/or vaporize them, solvent treatment to dissolve them, or other process that selectively removes the inserts from the molded core. A final core 100 remains as shown in FIG. 4 with core interior and exterior features 100 a-100 h formed by the respective inserts 30 a-30 h that have been selectively removed.

The next ceramic core is produced using fresh (un-used) tooling liners 20 a, 20 b and optional fresh tooling inserts 30. That is, the fugitive tooling liners and inserts can be used in one production cycle (e.g. ceramic injection cycle) to make a single ceramic core and then replaced with fresh (un-used) tooling liners and optional inserts. Alternately, the fugitive tooling liners may be left in the back-up body 10 and reused if the tooling liners are in acceptable condition to this end. That is, the fugitive tooling liners and inserts can be used in multiple production cycles (e.g. ceramic slurry injection cycles) to make multiple ceramic cores and then replaced with fresh (un-used) tooling liners and optional inserts when the tooling liners are not longer in acceptable condition to this end. However, when back-locked core features are produced, the tooling liners are used only in one production cycle since they are destroyed to separate them from the core.

It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the present invention described above without departing from the spirit and scope of the invention as set forth in the appended claims. 

1. Tooling for making a ceramic core, comprising a back-up body and one or more fugitive tooling liners disposed in the back-up body to form at least a portion of a core-shaped cavity.
 2. The tooling of claim 1 wherein the back-up body comprises multiple parts positionable to form a tooling cavity to receive the tooling liners.
 3. The tooling of claim 2 wherein first and second fugitive tooling liners are placed in the tooling cavity and each first and second tooling liner includes an outer surface having a simple geometry to match that of an adjacent inner support surface of an adjacent part of the back-up body and an inner surface that is configured to form at least a portion of the desired core surface features when the tooling liners are placed in the back-up body.
 4. The tooling of claim 3 wherein the inner surfaces of the first and second fugitive tooling liners form all of the core surface.
 5. The tooling of claim 3 wherein the inner surfaces of the first and second fugitive tooling liners form a portion of the core surface and surfaces of the back-up body form remaining core surface.
 6. The tooling of claim 1 wherein the back-up body includes easily machined interior surfaces.
 7. The tooling of claim 6 wherein the tooling liners include surfaces that mate with respective easily machined surfaces of the back-up body.
 8. The tooling of claim 1 wherein the tooling liners comprise a polymer.
 9. The tooling of claim 1 including one or more fugitive inserts between the tooling liners.
 10. The tooling of claim 1 including one or more fugitive inserts on the tooling liners.
 11. The tooling of claim 1 wherein the tooling liners form an airfoil-shaped cavity.
 12. A method of making a ceramic core, comprising introducing a fluid ceramic core material into a core-shaped cavity formed at least in part by one or more fugitive tooling liners in a back-up body, removing the ceramic core from the cavity, and removing the one or more fugitive tooling liners from the back-up body.
 13. The method of claim 12 wherein the steps thereof are repeated using fresh, un-used tooling liners to make another ceramic core.
 14. The method of claim 12 wherein the steps thereof are repeated using the same tooling liners to make another ceramic core.
 15. The method of claim 12 wherein the fluid ceramic material is introduced under pressure into the cavity.
 16. The method of claim 12 including placing the tool liners in the back-up body so that surfaces of the tooling liners conform to easily machined surfaces of the back-up body.
 17. The method of claim 12 including injection molding the tooling liners before placing them in the back-up body.
 18. The method of claim 12 including discarding the used tooling liners.
 19. The method of claim 12 wherein the core-shaped cavity is formed to have an airfoil shape.
 20. The method of claim 12 including placing one or more fugitive inserts between the tooling liners.
 21. The method of claim 12 including placing one or more fugitive inserts on the tooling liners. 